I notice a lot of trends in StackOverflow--lately I've noticed a pretty massive swing to android--it has more questions than Java and iPhone combined right now.

This doesn't exactly mean any one thing--It could mean that the iPhone is much easier to program or it could mean that Android is more popular right now or that Android is easier allowing more people to try--but regardless the info would still be really interesting to see.

I'd love to see how many questions are tagged C++ vs C# vs Java, what percentage of C questions involve pointers, what other tags are most common on Java questions, etc.

This info would be useful both as instantaneous counts and graphs over time.

Has anyone made such a tool--or is there one hidden her somewhere? If not I'd like to suggest one be considered.

[android] has 50k questions, while [java] has 108k and [iphone] has 70k -- where are you getting your numbers?
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GabeMar 27 '11 at 2:47

They may be referring to instantaneous numbers, but while [android] beats [iphone] this week, 1710 to 1274, it does not beat [java] at 2097. One reason for a greater rate of Android questions is that there is more to ask, because iPhone has traditionally had a strong base of questions here and so many iPhone-related questions have already been asked in one form or another. In fact, I can usually blow all my close votes in a day simply on the duplicate [iphone] questions coming in.
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Brad LarsonMar 27 '11 at 3:43

Statistics like you request were generated by Greg Hewgill a while ago and presented in the question Tag trends by week, so this is close to duplicating that question.
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Brad LarsonMar 27 '11 at 3:46

Keep in mind, though, that iOS has replaced iPhone, so you might need to add the iOS and iPhone tags together to get a more complete picture. You'll notice that about the time iPhone starts dipping, iOS was introduced, and starts trending upwards: